Differences in national income equality around the world as measured by the national Gini coefficient. The Gini coefficient is a number between 0 and 1, where 0 corresponds with perfect equality (where everyone has the same income) and 1 corresponds with absolute inequality (where one person has all the income, and everyone else has zero income).

Some studies have emphasized inequality as a growing social problem.[3] Too much inequality can be destructive,[4][5] because income inequality and wealth concentration can hinder long term growth.[6][7][8] Early statistical studies comparing inequality to economic growth had been inconclusive,[9] however in 2011, International Monetary Fund economists showed that greater income equality--less inequality--increased the duration of countries' economic growth spells more than free trade, low government corruption, foreign investment, or low foreign debt.[10]

Economic inequality varies between societies, historical periods, economic structures and systems. The term can refer to cross sectional distribution of income or wealth at any particular period, or to the lifetime income and wealth over longer periods of time.[11] There are various numerical indices for measuring economic inequality. A widely used one is the Gini coefficient, but there are also many other methods.

Economists generally think of three metrics of economic disparity: wealth, income, and consumption.[1] A skilled professional may have low wealth and low income as student, low wealth and high earnings in the beginning of the career, and high wealth and low earnings after the career. People's preferences determine whether they consume earnings immediately or defer consumption to the future. The distinction is also important at the level of economy:

There are economies with high income inequality and relatively low wealth inequality (such as Japan and Italy).[1]

There are economies with relatively low income inequality and high wealth inequality (such as Switzerland and Denmark).[1]

There are many different ways to measure income inequality and wealth inequality. Different choices lead to different results. OECD has inspected the following 8 types of income inequality concepts:[12]

There are many challenges in comparing data between economies, or in a single economy in different years. Examples of challenges include:

Data can be based on joint taxation of couples (e.g. France, Germany, Ireland, Netherlands, Portugal and Switzerland) or individual taxation (e.g. Australia, Canada, Italy, Japan, New Zealand, Spain, the UK).[12]

The tax authorities generally only collect information on income that is potentially taxable.[12]

The precise definition of gross income varies from country to country. There are differences when it comes to inclusion of pension entitlements and other savings, and benefits such as employer provided health insurance.[12]

Differences when it comes under-declaration of income and/or wealth in tax filings.[12]

A special event like an exit from business may lead to a very high income in one year, but much lower income in other years of the person's lifetime.[12]

Changes in the structure of households can play an important role. Single-headed households in OECD countries have risen from an average of 15% in the late 1980s to 20% in the mid-2000s, resulting in higher inequality.

Assortative mating refers to the phenomenon of people marrying people with similar background, for example doctors marrying doctors rather than nurses. OECD found out that 40% of couples where both partners work belonged to the same or neighbouring earnings deciles compared with 33% some 20 years before.[12]

A 2011 OECD study investigated economic inequality in Argentina, Brazil, China, India, Indonesia, Russia and South Africa. It concluded that key sources of inequality in these countries include "a large, persistent informal sector, widespread regional divides (e.g. urban-rural), gaps in access to education, and barriers to employment and career progression for women."[12]

A study by the World Institute for Development Economics Research at United Nations University reports that the richest 1% of adults alone owned 40% of global assets in the year 2000. The three richest people in the world possess more financial assets than the lowest 48 nations combined.[15] The combined wealth of the "10 million dollar millionaires" grew to nearly $41 trillion in 2008.[16] A January 2014 report by Oxfam claims that the 85 wealthiest individuals in the world have a combined wealth equal to that of the bottom 50% of the world's population, or about 3.5 billion people.[17][18][19][20][21] According to a Los Angeles Times analysis of the report, the wealthiest 1% owns 46% of the world's wealth; the 85 richest people, a small part of the wealthiest 1%, own about 0.7% of the human population's wealth, which is the same as the bottom half of the population.[22] More recently, in January 2015, Oxfam reported that the wealthiest 1 percent will own more than half of the global wealth by 2016.[23][24] An October 2014 study by Credit Suisse also claims that the top 1% now own nearly half of the world's wealth and that the accelerating disparity could trigger a recession.[25]

The existing data and estimates suggest a large increase in international (and more generally inter-macroregional) component between 1820 and 1960. It might have slightly decreased since that time at the expense of increasing inequality within countries.[33]

The United Nations Development Programme in 2014 asserted that greater investments in social security, jobs and laws that protect vulnerable populations are necessary to prevent widening income inequality....[34]

There is a significant difference in the measured wealth distribution and the public’s understanding of wealth distribution. Michael Norton of the Harvard Business School and Dan Ariely of the Departement of Psychology at Duke University found this to be true in their research, done in 2011. The actual wealth going to the top quintile in 2011 was around 84% where as the average amount of wealth that the general public estimated to go to the top quintile was around 58%.[35]

There are many reasons for economic inequality within societies. Recent growth in overall income inequality, at least within the OECD countries, has been driven mostly by increasing inequality in wages and salaries.[14]

Economist Thomas Piketty, who specializes in the study of economic inequality, argues that widening economic disparity is an inevitable phenomenon of free marketcapitalism when the rate of return of capital (r) is greater than the rate of growth of the economy (g).[36]

Neoclassical economics views inequalities in the distribution of income as arising from differences in productivity, and attribute rising inequality to rising differences in the productivity of different groups of workers. In this perspective, wages and profits are determined by the marginal productivity of each individual in the economy. Thus rising inequalities are merely a reflection of the productivity gap between highly-paid professions and lower-paid professions.[45]

In Marxian economic analysis, rising income inequality is an inherent feature of capitalism. In this analysis, capitalist firms increasingly substitute workers for capital equipment under competitive pressures to reduce costs and maximize profit. Over the long-term, this trend increases the organic composition of capital, meaning that less labor inputs (workers) are required in proportion to capital inputs, increasing unemployment and the size of the reserve army of labour. This process exerts a downward pressure on wages. The substitution of labor for capital equipment (job automation) increases productivity per worker and thus profits for the capitalist class, resulting in a situation of relatively stagnant wages for the working class amidst rising levels of property income for the capitalist class.[46]

Therefore, Marxian economics attributes rising inequality to both the ownership structure of capitalist economies and to rising job automation conflicting with the requirements of the wage labor system.

A major cause of economic inequality within modern market economies is the determination of wages by the market. Some small part of economic inequality is caused by the differences in the supply and demand for different types of work. However, where competition is imperfect; information unevenly distributed; opportunities to acquire education and skills unequal; and since many such imperfect conditions exist in virtually every market, there is in fact little presumption that markets are in general efficient. This means that there is an enormous potential role for government to correct these market failures.[47]

In a purely capitalist mode of production (i.e. where professional and labor organizations cannot limit the number of workers) the workers wages will not be controlled by these organizations, or by the employer, but rather by the market. Wages work in the same way as prices for any other good. Thus, wages can be considered as a function of market price of skill. And therefore, inequality is driven by this price. Under the law of supply and demand, the price of skill is determined by a race between the demand for the skilled worker and the supply of the skilled worker. "On the other hand, markets can also concentrate wealth, pass environmental costs on to society, and abuse workers and consumers." "Markets, by themselves, even when they are stable, often lead to high levels of inequality, outcomes that are widely viewed as unfair."[48] Employers who offer a below market wage will find that their business is chronically understaffed. Their competitors will take advantage of the situation by offering a higher wage to snatch up the best of their labor. For a businessman who has the profit motive as the prime interest, it is a losing proposition to offer below or above market wages to workers.[49]

A job where there are many workers willing to work a large amount of time (high supply) competing for a job that few require (low demand) will result in a low wage for that job. This is because competition between workers drives down the wage. An example of this would be jobs such as dish-washing or customer service. Competition amongst workers tends to drive down wages due to the expendable nature of the worker in relation to his or her particular job. A job where there are few able or willing workers (low supply), but a large need for the positions (high demand), will result in high wages for that job. This is because competition between employers for employees will drive up the wage. Examples of this would include jobs that require highly developed skills, rare abilities, or a high level of risk. Competition amongst employers tends to drive up wages due to the nature of the job, since there is a relative shortage of workers for the particular position. Professional and labor organizations may limit the supply of workers which results in higher demand and greater incomes for members. Members may also receive higher wages through collective bargaining, political influence, or corruption.[50]

These supply and demand interactions result in a gradation of wage levels within society that significantly influence economic inequality. Polarization of wages does not explain the accumulation of wealth and very high incomes among the 1%. Joseph Stiglitz believes that "It is plain that markets must be tamed and tempered to make sure they work to the benefit of most citizens."[51]

Another cause is the rate at which income is taxed coupled with the progressivity of the tax system. A progressive tax is a tax by which the tax rate increases as the taxable base amount increases.[52][53][54][55][56] In a progressive tax system, the level of the top tax rate will often have a direct impact on the level of inequality within a society, either increasing it or decreasing it, provided that income does not change as a result of the change in tax regime. Additionally, steeper tax progressivity applied to social spending can result in a more equal distribution of income across the board.[57] The difference between the Gini index for an income distribution before taxation and the Gini index after taxation is an indicator for the effects of such taxation.[58]

There is debate between politicians and economists over the role of tax policy in mitigating or exacerbating wealth inequality. Economists such as Paul Krugman, Peter Orszag, and Emmanuel Saez have argued that tax policy in the post World War II era has indeed increased income inequality by enabling the wealthiest Americans far greater access to capital than lower-income ones.[38]

Illustration from a 1916 advertisement for a vocational school in the back of a US magazine. Education has been seen as a key to higher income, and this advertisement appealed to Americans' belief in the possibility of self-betterment, as well as threatening the consequences of downward mobility in the great income inequality existing during the Industrial Revolution.

An important factor in the creation of inequality is variation in individuals' access to education.[59] Education, especially in an area where there is a high demand for workers, creates high wages for those with this education,[60] however, increases in education first increase and then decrease growth as well as income inequality. As a result, those who are unable to afford an education, or choose not to pursue optional education, generally receive much lower wages. The justification for this is that a lack of education leads directly to lower incomes, and thus lower aggregate savings and investment. In particular, the increase in family income and wealth inequality leads to greater dispersion of educational attainment, primarily because those at the bottom of the educational distribution have fallen further below the average level of education. Conversely, education raises incomes and promotes growth because it helps to unleash the productive potential of the poor.

In 2014, economists with the Standard & Poor's rating agency concluded that the widening disparity between the U.S.'s wealthiest citizens and the rest of the nation had slowed its recovery from the 2008-2009 recession and made it more prone to boom-and-bust cycles. To partially remedy the wealth gap and the resulting slow growth, S&P recommended increasing access to education. It estimated that if the average United States worker had completed just one more year of school, it would add an additional $105 billion in growth to the country's economy over five years.[61]

During the mass high school education movement from 1910–1940, there was an increase in skilled workers, which led to a decrease in the price of skilled labor. High school education during the period was designed to equip students with necessary skill sets to be able to perform at work. In fact, it differs from the present high school education, which is regarded as a stepping-stone to acquire college and advanced degrees. This decrease in wages caused a period of compression and decreased inequality between skilled and unskilled workers. Education is very important for the growth of the economy, however educational inequality in gender also influence towards the economy. Lagerlof and Galor stated that gender inequality in education can result to low economic growth, and continued gender inequality in education, thus creating a poverty trap. It is suggested that a large gap in male and female education may indicate backwardness and so may be associated with lower economic growth, which can explain why there is economic inequality between countries.

More of Barro studies also find that female secondary education is positively associated with growth. His findings show that countries with low female education; increasing it has little effect on economic growth, however in countries with high female education, increasing it significantly boosts economic growth. More and better education is a prerequisite for rapid economic development around the world. Education stimulates economic growth and improves people's lives through many channels.

By increasing the efficiency of the labour force it create better conditions for good governance, improving health and enhancing equality. Labor market success is linked to schooling achievement, the consequences of widening disparities in schooling is likely to be further increases in earnings inequality

John Schmitt and Ben Zipperer (2006) of the CEPR point to economic liberalism and the reduction of business regulation along with the decline of union membership as one of the causes of economic inequality. In an analysis of the effects of intensive Anglo-American liberal policies in comparison to continental European liberalism, where unions have remained strong, they concluded "The U.S. economic and social model is associated with substantial levels of social exclusion, including high levels of income inequality, high relative and absolute poverty rates, poor and unequal educational outcomes, poor health outcomes, and high rates of crime and incarceration. At the same time, the available evidence provides little support for the view that U.S.-style labor-market flexibility dramatically improves labor-market outcomes. Despite popular prejudices to the contrary, the U.S. economy consistently affords a lower level of economic mobility than all the continental European countries for which data is available."[64]

Sociologist Jake Rosenfield of the University of Washington asserts that the decline of organized labor in the United States has played a more significant role in expanding the income gap than technological changes and globalization, which were also experienced by other industrialized nations that didn't experience steep surges in inequality. He points out that nations with high rates of unionization, particularly in Scandinavia, have very low levels of inequality, and concludes "the historical pattern is clear; the cross-national pattern is clear: high inequality goes hand-in-hand with weak labor movements and vice-versa."[65]

A 2015 study by the International Monetary Fund found that the decline of unionization in many advanced economies starting in the 1980s has fueled rising income inequality.[66][67]

Trade liberalization may shift economic inequality from a global to a domestic scale.[68] When rich countries trade with poor countries, the low-skilled workers in the rich countries may see reduced wages as a result of the competition, while low-skilled workers in the poor countries may see increased wages. Trade economist Paul Krugman estimates that trade liberalisation has had a measurable effect on the rising inequality in the United States. He attributes this trend to increased trade with poor countries and the fragmentation of the means of production, resulting in low skilled jobs becoming more tradeable. However, he concedes that the effect of trade on inequality in America is minor when compared to other causes, such as technological innovation, a view shared by other experts. Lawrence Katz estimates that trade has only accounted for 5-15% of rising income inequality. Robert Lawrence argues that technological innovation and automation has meant that low-skilled jobs have been replaced by machine labor in wealthier nations, and that wealthier countries no longer have significant numbers of low-skilled manufacturing workers that could be affected by competition from poor countries.[68]

The gender gap in median earnings of full-time employees according to the OECD 2008[69]

In many countries, there is a gender income gap which favors males in the labor market. For example, the median full-time salary for U.S. women is 77% of that of U.S. men. Several factors other than discrimination may contribute to this gap. On average, women are more likely than men to consider factors other than pay when looking for work, and may be less willing to travel or relocate.[70][71]Thomas Sowell, in his book Knowledge and Decisions, claims that this difference is due to women not taking jobs due to marriage or pregnancy, but income studies show that that does not explain the entire difference. A U.S. Census's report stated that in US once other factors are accounted for there is still a difference in earnings between women and men.[72] The income gap in other countries ranges from 53% in Botswana to -40% in Bahrain.[73]

Economist Simon Kuznets argued that levels of economic inequality are in large part the result of stages of development. According to Kuznets, countries with low levels of development have relatively equal distributions of wealth. As a country develops, it acquires more capital, which leads to the owners of this capital having more wealth and income and introducing inequality. Eventually, through various possible redistribution mechanisms such as social welfare programs, more developed countries move back to lower levels of inequality.

Plotting the relationship between level of income and inequality, Kuznets saw middle-income developing economies level of inequality bulging out to form what is now known as the Kuznets curve. Kuznets demonstrated this relationship using cross-sectional data. However, more recent testing of this theory with superior panel data has shown it to be very weak. Kuznets' curve predicts that income inequality will eventually decrease given time. As an example, income inequality did fall in the United States during its High school movement from 1910 to 1940 and thereafter.[citation needed] However, recent data shows that the level of income inequality began to rise after the 1970s. This does not necessarily disprove Kuznets' theory. It may be possible that another Kuznets' cycle is occurring, specifically the move from the manufacturing sector to the service sector. This implies that it may be possible for multiple Kuznets' cycles to be in effect at any given time.

Related to cultural issues, diversity of preferences within a society may contribute to economic inequality. When faced with the choice between working harder to earn more money or enjoying more leisure time, equally capable individuals with identical earning potential may choose different strategies.[citation needed] The trade-off between work and leisure is particularly important in the supply side of the labor market in labor economics.[citation needed]

Likewise, individuals in a society often have different levels of risk aversion. When equally-able individuals undertake risky activities with the potential of large payoffs, such as starting new businesses, some ventures succeed and some fail. The presence of both successful and unsuccessful ventures in a society results in economic inequality even when all individuals are identical.[citation needed]

Wealth concentration is a theoretical[according to whom?] process by which, under certain conditions, newly created wealth concentrates in the possession of already-wealthy individuals or entities. According to this theory, those who already hold wealth have the means to invest in new sources of creating wealth or to otherwise leverage the accumulation of wealth, thus are the beneficiaries of the new wealth. Over time, wealth condensation can significantly contribute to the persistence of inequality within society. Thomas Piketty in his book Capital in the Twenty-First Century argues that the fundamental force for divergence is the usually greater return of capital (r) than economic growth (g), and that larger fortunes generate higher returns [pp. 384 Table 12.2, U.S. university endowment size vs. real annual rate of return]

Economist Joseph Stiglitz argues that rather than explaining concentrations of wealth and income, market forces should serve as a brake on such concentration, which may better be explained by the non-market force known as "rent-seeking". While the market will bid up compensation for rare and desired skills to reward wealth creation, greater productivity, etc., it will also prevent successful entrepreneurs from earning excess profits by fostering competition to cut prices, profits and large compensation.[76] A better explainer of growing inequality, according to Stiglitz, is the use of political power generated by wealth by certain groups to shape government policies financially beneficial to them. This process, known to economists as rent-seeking, brings income not from creation of wealth but from "grabbing a larger share of the wealth that would otherwise have been produced without their effort"[77]

Rent seeking is often thought to be the province of societies with weak institutions and weak rule of law, but Stiglitz believes there is no shortage of it in developed societies such as the United States. Examples of rent seeking leading to inequality include

securing government tolerance of monopoly power (The richest person in the world in 2011, Carlos Slim, controlled Mexico's newly privatized telecommunication industry[82]).

Since rent seeking aims to "pluck the goose to obtain the largest amount of feathers with the least possible amount of hissing" – it is by nature obscure, avoiding public spotlight in legal fine print, or camouflaged its extraction with widely accepted rationalizations (markets are naturally competitive and so need no government regulation against monopolies[83]).

Countries with a left-leaninglegislature have lower levels of inequality.[86][87] Many factors constrain economic inequality – they may be divided into two classes: government sponsored, and market driven. The relative merits and effectiveness of each approach is a subject of debate.

Public education: increasing the supply of skilled labor and reducing income inequality due to education differentials.[88]

Progressive taxation: the rich are taxed proportionally more than the poor, reducing the amount of income inequality in society if the change in taxation does not cause changes in income.[89]

Market forces outside of government intervention that can reduce economic inequality include:

propensity to spend: with rising wealth & income, a person may spend more. In an extreme example, if one person owned everything, they would immediately need to hire people to maintain their properties, thus reducing the wealth concentration.[90]

Effects of inequality researchers have found include higher rates of health and social problems, and lower rates of social goods,[91] a lower level of economic utility in society from resources devoted on high-end consumption,[92] and even a lower level of economic growth when human capital is neglected for high-end consumption.[93] For the top 21 industrialised countries, counting each person equally, life expectancy is lower in more unequal countries (r = -.907).[94] A similar relationship exists among US states (r = -.620).[95]

2013 Economics Nobel prize winner Robert J. Shiller said that rising inequality in the United States and elsewhere is the most important problem.[96] Increasing inequality harms economic growth.[97] High and persistent unemployment, in which inequality increases, has a negative effect on subsequent long-run economic growth. Unemployment can harm growth not only because it is a waste of resources, but also because it generates redistributive pressures and subsequent distortions, drives people to poverty, constrains liquidity limiting labor mobility, and erodes self-esteem promoting social dislocation, unrest and conflict. Policies aiming at controlling unemployment and in particular at reducing its inequality-associated effects support economic growth.[5]

The economic stratification of society into "elites" and "masses" played a central role in the collapse of other advanced civilizations such as the Roman, Han and Gupta empires.[98]

Income inequality and mortality in 282 metropolitan areas of the United States. Mortality is strongly associated with higher income inequality, but, within levels of income inequality, not with per capita income.

For most of human history higher material living standards – full stomachs, access to clean water and warmth from fuel – led to better health and longer lives.[91] This pattern of higher incomes-longer lives still holds among poorer countries, where life expectancy increases rapidly as per capita income increases, but in recent decades it has slowed down among middle income countries and plateaued among the richest thirty or so countries in the world.[100]Americans live no longer on average (about 77 years in 2004) than Greeks (78 years) or New Zealanders (78), though the USA has a higher GDP per capita. Life expectancy in Sweden (80 years) and Japan (82) – where income was more equally distributed – was longer.[101][102]

In recent years the characteristic that has strongly correlated with health in developed countries is income inequality. Creating an index of "Health and Social Problems" from nine factors, authors Richard Wilkinson and Kate Pickett found health and social problems "more common in countries with bigger income inequalities",[103][104] and more common among states in the US with larger income inequalities.[105] Other studies have confirmed this relationship. The UNICEF index of "child well-being in rich countries", studying 40 indicators in 22 countries, correlates with greater equality but not per capita income.[106]

Pickett and Wilkinson argue that inequality and social stratification lead to higher levels of psychosocial stress and status anxiety which can lead to depression, chemical dependency, less community life, parenting problems and stress-related diseases.[107]

Research has shown an inverse link between income inequality and social cohesion. In more equal societies, people are much more likely to trust each other, measures of social capital (the benefits of goodwill, fellowship, mutual sympathy and social connectedness among groups who make up a social units) suggest greater community involvement, and homicide rates are consistently lower.

Comparing results from the question "would others take advantage of you if they got the chance?" in U.S General Social Survey and statistics on income inequality, Eric Uslaner and Mitchell Brown found there is a high correlation between the amount of trust in society and the amount of income equality.[108] A 2008 article by Andersen and Fetner also found a strong relationship between economic inequality within and across countries and tolerance for 35 democracies.

Community and equality are mutually reinforcing... Social capital and economic inequality moved in tandem through most of the twentieth century. In terms of the distribution of wealth and income, America in the 1950s and 1960s was more egalitarian than it had been in more than a century... [T]hose same decades were also the high point of social connectedness and civic engagement. Record highs in equality and social capital coincided. Conversely, the last third of the twentieth century was a time of growing inequality and eroding social capital... The timing of the two trends is striking: somewhere around 1965–70 America reversed course and started becoming both less just economically and less well connected socially and politically.[111]

Albrekt Larsen has advanced this explanation by a comparative study of how trust increased in Denmark and Sweden in the latter part of the 20th century while it decreased in the US and UK. It is argued that inequality levels influence how citizens imagine the trustworthiness of fellow citizens. In this model social trust is not about relations to people you meet (as in Putnam's model) but about people you imagine.[112]

The economist Joseph Stiglitz has argued that economic inequality has led to distrust of business and government.[113]

Crime rate has also been shown to be correlated with inequality in society. Most studies looking into the relationship have concentrated on homicides – since homicides are almost identically defined across all nations and jurisdictions. There have been over fifty studies showing tendencies for violence to be more common in societies where income differences are larger. Research has been conducted comparing developed countries with undeveloped countries, as well as studying areas within countries. Daly et al. 2001[114] found that among U.SStates and CanadianProvinces there is a tenfold difference in homicide rates related to inequality. They estimated that about half of all variation in homicide rates can be accounted for by differences in the amount of inequality in each province or state. Fajnzylber et al. (2002) found a similar relationship worldwide. Among comments in academic literature on the relationship between homicides and inequality are:

The most consistent finding in cross-national research on homicides has been that of a positive association between income inequality and homicides.[115]

Economic inequality is positively and significantly related to rates of homicide despite an extensive list of conceptually relevant controls. The fact that this relationship is found with the most recent data and using a different measure of economic inequality from previous research, suggests that the finding is very robust.[116]

Higher income inequality led to less of all forms of social, cultural, and civic participation among the less wealthy.[117] When inequality is higher the poor do not shift to less expensive forms of participation.[118]

Following the utilitarian principle of seeking the greatest good for the greatest number – economic inequality is problematic. A house that provides less utility to a millionaire as a summer home than it would to a homeless family of five, is an example of reduced "distributive efficiency" within society, that decreasesmarginal utility of wealth and thus the sum total of personal utility. An additional dollar spent by a poor person will go to things providing a great deal of utility to that person, such as basic necessities like food, water, and healthcare; while, an additional dollar spent by a much richer person will very likely go to luxury items providing relatively less utility to that person. Thus, the marginal utility of wealth per person ("the additional dollar") decreases as a person becomes richer. From this standpoint, for any given amount of wealth in society, a society with more equality will have higher aggregate utility. Some studies[92][119] have found evidence for this theory, noting that in societies where inequality is lower, population-wide satisfaction and happiness tend to be higher.

... it is evident that any transference of income from a relatively rich man to a relatively poor man of similar temperament, since it enables more intense wants, to be satisfied at the expense of less intense wants, must increase the aggregate sum of satisfaction. The old "law of diminishing utility" thus leads securely to the proposition: Any cause which increases the absolute share of real income in the hands of the poor, provided that it does not lead to a contraction in the size of the national dividend from any point of view, will, in general, increase economic welfare.[120]

Philosopher David Schmidtz argues that maximizing the sum of individual utilities will harm incentives to produce.

A society that takes Joe Rich’s second unit [of corn] is taking that unit away from someone who . . . has nothing better to do than plant it and giving it to someone who . . . does have something better to do with it. That sounds good, but in the process, the society takes seed corn out of production and diverts it to food, thereby cannibalizing itself.[121]

However, in addition to the diminishing marginal utility of unequal distribution, Pigou and others point out that a "keeping up with the Joneses" effect among the well off may lead to greater inequality and use of resources for no greater return in utility.

a larger proportion of the satisfaction yielded by the incomes of rich people comes from their relative, rather than from their absolute, amount. This part of it will not be destroyed if the incomes of all rich people are diminished together. The loss of economic welfare suffered by the rich when command over resources is transferred from them to the poor will, therefore, be substantially smaller relatively to the gain of economic welfare to the poor than a consideration of the law of diminishing utility taken by itself suggests.[120]

When the goal is to own the biggest yacht – rather than a boat with certain features – there is no greater benefit from owning 100 metre long boat than a 20 m one as long as it is bigger than your rival. Economist Robert H. Frank compare the situation to that of male elks who use their antlers to spar with other males for mating rights.

The pressure to have bigger ones than your rivals leads to an arms race that consumes resources that could have been used more efficiently for other things, such as fighting off disease. As a result, every male ends up with a cumbersome and expensive pair of antlers, ... and "life is more miserable for bull elk as a group."[122]

Income inequality lowers aggregate demand, leading to increasingly large segments of formerly middle class consumers unable to afford as many luxury and essential goods and services.[123] This pushes production and overall employment down.[5]

Conservative researchers have argued that income inequality is not significant because consumption, rather than income should be the measure of inequality, and inequality of consumption is less extreme than inequality of income in the US. Will Wilkinson of the libertarianCato Institute states that "the weight of the evidence shows that the run-up in consumption inequality has been considerably less dramatic than the rise in income inequality," and consumption is more important than income.[124] According to Johnson, Smeeding, and Tory, consumption inequality was actually lower in 2001 than it was in 1986.[125][126] The debate is summarized in "The Hidden Prosperity of the Poor" by journalist Thomas B. Edsall.[127] Other studies have not found consumption inequality less dramatic than household income inequality,[128][129] and the CBO's study found consumption data not "adequately" capturing "consumption by high-income households" as it does their income, though it did agree that household consumption numbers show more equal distribution than household income.[130]

Others dispute the importance of consumption over income, pointing out that if middle and lower income are consuming more than they earn it is because they are saving less or going deeper into debt.[131] Income inequality has been the driving factor in the growing household debt,[128][132] as high earners bid up the price of real estate and middle income earners go deeper into debt trying to maintain what once was a middle class lifestyle.[133]

Central Banking economist Raghuram Rajan argues that "systematic economic inequalities, within the United States and around the world, have created deep financial 'fault lines' that have made [financial] crises more likely to happen than in the past" – the Financial crisis of 2007–08 being the most recent example.[134] To compensate for stagnating and declining purchasing power, political pressure has developed to extend easier credit to the lower and middle income earners – particularly to buy homes – and easier credit in general to keep unemployment rates low. This has given the American economy a tendency to go "from bubble to bubble" fueled by unsustainable monetary stimulation.[135]

Some modern economic theories, such as the neoclassical school, have suggested that a functioning economy entails a certain level of unemployment. These theories argue that unemployment benefits must be below the wage level to provide an incentive to work, thereby mandating inequality. Such theories state additionally that the unemployment rate cannot reduce to zero.[citation needed]

Some economists believe that one of the main reasons that inequality might induce economic incentive is because material well-being and conspicuous consumption relate to status. In this view, high stratification of income (high inequality) creates high amounts of social stratification, leading to greater competition for status.

[W]hat is the end of avarice and ambition, of the pursuit of wealth, of power, and pre-eminence? Is it to supply the necessities of nature? The wages of the meanest labourer can supply them... [W]hy should those who have been educated in the higher ranks of life, regard it as worse than death, to be reduced to live, even without labour, upon the same simple fare with him, to dwell under the same lowly roof, and to be clothed in the same humble attire? From whence, then, arises that emulation which runs through all the different ranks of men, and what are the advantages which we propose by that great purpose of human life which we call bettering our condition? To be observed, to be attended to, to be taken notice of with sympathy, complacency, and approbation, are all the advantages which we can propose to derive from it. It is the vanity, not the ease, or the pleasure, which interests us.[137]

Modern sociologists and economists such as Juliet Schor and Robert H. Frank have studied the extent to which economic activity is fueled by the ability of consumption to represent social status. Schor, in The Overspent American, argues that the increasing inequality during the 1980s and 1990s strongly accounts for increasing aspirations of income, increased consumption, decreased savings, and increased debt.

In the book Luxury Fever, Robert H. Frank argues that satisfaction with levels of income is much more strongly affected by how someone's income compares with others than its absolute level. Frank gives the example of instructions to a yacht architect by a customer – shipping magnate Stavros Niarchos – to make Niarchos' new yacht 50 feet longer than that of rival magnate Aristotle Onassis. Niarchos did not specify or reportedly even know the exact length of Onassis's yacht.[138][139]

According to International Monetary Fund economists, inequality in wealth and income is negatively correlated with subsequent economic growth.[10] A strong demand for redistribution will occur in societies where much of the population does not have access to productive resources. Rational voters have to internalize this dynamic problem of social choice.[140] 2013 Economics Nobel prize winner Robert J. Shiller, who shares the IMF's view, said that rising inequality in the United States and elsewhere is the most important problem being faced in the U.S. and elsewhere in the world.[141] High levels of inequality prevent not just economic prosperity, but also the quality of a country's institutions and high levels of education.[4]

According to economists David Castells-Quintana and Vicente Royuela, increasing inequality harms economic growth.[5] High and persistent unemployment, in which inequality increases, has a negative effect on subsequent long-run economic growth according to research by David Castells-Quintana.[5] Unemployment can harm growth not only because it is a waste of resources, but also because it generates redistributive pressures and subsequent distortions, drives people to poverty, constrains liquidity limiting labor mobility, and erodes self-esteem promoting social dislocation, unrest and conflict.[5] Policies aiming at controlling unemployment and in particular at reducing its inequality-associated effects support economic growth.[5]

Berg and Ostry of the International Monetary Fund found that of the factors affecting the duration of growth spells in developed and developing countries, income equality is more beneficial than trade openness, sound political institutions, or foreign investment.[10][142]

Some theories popular from the 1970s to 2011 stated that inequality had a positive effect on economic development.[10][142] Savings by the wealthy, which increases with inequality, was thought to offset reduced consumer demand.[143] A study by the International Monetary Fund found that the analysis based on comparing yearly equality figures to yearly growth rates was flawed and misleading because it takes several years for the effects of equality changes to manifest in economic growth changes.[9] IMF economists Andrew G. Berg and Jonathan D. Ostry found a strong association between lower levels of inequality in developing countries and sustained periods of economic growth. Developing countries with high inequality have "succeeded in initiating growth at high rates for a few years" but "longer growth spells are robustly associated with more equality in the income distribution."[142]

Economist Joseph Stiglitz presented evidence in 2009 review that both global inequality and inequality within countries prevent growth by limiting aggregate demand.[6] A 1999 review in the Journal of Economic Literature states high inequality lowers growth, perhaps because it increases social and political instability.[7] A 1992 World Bank report published in the Journal of Development Economics said that inequality "is negatively, and robustly, correlated with growth. This result is not highly dependent upon assumptions about either the form of the growth regression or the measure of inequality."[8]

In 1993, Galor and Zeira showed that inequality in the presence of credit market imperfections has a long lasting detrimental effect on human capital formation and economic development.[144] A study by Perotti (1996) examines the channels through which inequality may affect economic growth. He shows that in accordance with the credit market imperfection approach, inequality is associated with lower level of human capital formation (education, experience, apprenticeship) and higher level of fertility, while lower level of human capital is associated with lower growth and lower levels of economic growth. In contrast, his examination of the political economy channel refutes the political economy mechanism. He demonstrates that inequality is associated with lower levels of taxation, while lower levels of taxation, contrary to the theories, are associated with lower level of economic growth[145]

The political economy approach, developed by Alesina and Rodrik (1994) and Persson and Tabellini (1994), argues that inequality is harmful for economic development because inequality generates a pressure to adopt redistributive policies that have an adverse effect on investment and economic growth.[140][146]

Research by economist Muhammad Dandume Yusuf on the relationship between income inequality and growth in Nigeria (2013) suggests that "economic growth rises with inequality of income".[147] According to economist Ruth-Aida Nahum, whose paper studied Swedish counties between 1960 and 2000, she found a positive impact of inequality on growth with lead times of five years or less, but no correlation after ten years.[148] Studies of larger data sets have found no correlations for any fixed lead time,[9] and a negative impact on the duration of growth.[10]

According to economist Branko Milanovic, while traditionally economists thought inequality was good for growth

"The view that income inequality harms growth – or that improved equality can help sustain growth – has become more widely held in recent years. ... The main reason for this shift is the increasing importance of human capital in development. When physical capital mattered most, savings and investments were key. Then it was important to have a large contingent of rich people who could save a greater proportion of their income than the poor and invest it in physical capital. But now that human capital is scarcer than machines, widespread education has become the secret to growth."[93]

"Broadly accessible education" is both difficult to achieve when income distribution is uneven and tends to reduce "income gaps between skilled and unskilled labor."

The sovereign-debt economic problems of the late twenty-oughts do not seem to be correlated to redistribution policies in Europe. With the exception of Ireland, the countries at risk of default in 2011 (Greece, Italy, Spain, Portugal) were notable for their high Gini-measured levels of income inequality compared to other European countries. As measured by the Gini index, Greece as of 2008 had more income inequality than the economically healthy Germany.[149]

A number of researchers (David Rodda,[150] Jacob Vigdor,[151] and Janna Matlack), argue that a shortage of affordable housing – at least in the US – is caused in part by income inequality.[152] David Rodda[150][153] noted that from 1984 and 1991, the number of quality rental units decreased as the demand for higher quality housing increased (Rhoda 1994:148).[150] Through gentrification of older neighbourhoods, for example, in East New York, rental prices increased rapidly as landlords found new residents willing to pay higher market rate for housing and left lower income families without rental units. The ad valorem property tax policy combined with rising prices made it difficult or impossible for low income residents to keep pace.[154]

Firstly, certain costs are difficult to avoid and are shared by everyone, such as the costs of housing, pensions, education and health care.[155] If the state does not provide these services, then for those on lower incomes, the costs must be borrowed and often those on lower incomes are those who are worse equipped to manage their finances.[155] Secondly, aspirational consumption describes the process of middle income earners aspiring to achieve the standards of living enjoyed by their wealthier counterparts and one method of achieving this aspiration is by taking on debt.[155] The result leads to even greater inequality and potential economic instability.[155]

Oxfam asserts that worsening inequality is impeding the fight against global poverty. A 2013 report from the group stated that the $240 billion added to the fortunes of the world's richest billionaires in 2012 was enough to end extreme poverty four times over. Oxfam Executive Director Jeremy Hobbs said that "We can no longer pretend that the creation of wealth for a few will inevitably benefit the many – too often the reverse is true."[156][157][158]

The smaller the economic inequality, the more waste and pollution is created, resulting in many cases, in more environmental degradation. This can be explained by the fact that as the poor people in the society become more wealthy, it increases their yearly carbon emissions. This relation is expressed by the Environmental Kuznets Curve (EKC).[161][162][163][164] It should be noted here however that in certain cases, with great economic inequality, there is nonetheless not more waste and pollution created as the waste/pollution is cleaned up better afterwards (water treatment, filtering, ...)[165].... Also note that the whole of the increase in environmental degradation is the result of the increase of emissions per person being multiplied by a multiplier. If there were fewer people however, this multiplier would be lower, and thus the amount of environmental degradation would be lower as well. As such, the current high level of population has a large impact on this as well. If (as WWF argued), population levels would start to drop to a sustainable level (1/3 of current levels, so about 2 billion people[166]), human inequality can be addressed/corrected, while still not resulting in an increase of environmental damage.

Socialists attribute the vast disparities in wealth and income to the private ownership of the means of production by a class of owners, resulting in a situation where a small portion of the population receives unearned income in the form of property income by virtue of ownership titles in capital equipment, financial assets and corporate stock. In contrast, the vast majority of the population is dependent on income in the form of a wage or salary. In order to rectify this situation, socialists argue that the means of production should be publicly owned, so that income differentials would be reflective of individual contribution to the social product.[167]

Marxists ultimately predict the emergence of a communist society based on the common ownership of the means of production, where each individual citizen would have free access to the articles of consumption (From each according to his ability, to each according to his need).[168] According to Marxist philosophy, equality in this sense is essential for freedom because equal access to the output of the means of production frees individuals from dependent relationships, allowing them to transcend alienation.

Meritocracy favors an eventual society where an individual's success is a direct function of his merit, or contribution. Economic inequality would be a natural consequence of the wide range in individual skill, talent and effort in human population.[citation needed]

Most modern social liberals, including centrist or left-of-center political groups, believe that the capitalist economic system should be fundamentally preserved, but the status quo regarding the income gap must be reformed. Social liberals favor a capitalist system with active Keynesian macroeconomic policies and progressive taxation (to even out differences in income inequality).

The liberal champions of equality under the law were fully aware of the fact that men are born unequal and that it is precisely their inequality that generates social cooperation and civilization. Equality under the law was in their opinion not designed to correct the inexorable facts of the universe and to make natural inequality disappear. It was, on the contrary, the device to secure for the whole of mankind the maximum of benefits it can derive from it. Henceforth no man-made institutions should prevent a man from attaining that station in which he can best serve his fellow citizens.

Robert Nozick argued that government redistributes wealth by force (usually in the form of taxation), and that the ideal moral society would be one where all individuals are free from force. However, Nozick recognized that some modern economic inequalities were the result of forceful taking of property, and a certain amount of redistribution would be justified to compensate for this force but not because of the inequalities themselves. John Rawls argued in A Theory of Justice[42] that inequalities in the distribution of wealth are only justified when they improve society as a whole, including the poorest members. Rawls does not discuss the full implications of his theory of justice. Some see Rawls's argument as a justification for capitalism since even the poorest members of society theoretically benefit from increased innovations under capitalism; others believe only a strong welfare state can satisfy Rawls's theory of justice.

Classical liberal Milton Friedman believed that if government action is taken in pursuit of economic equality then political freedom would suffer. In a famous quote, he said:

A society that puts equality before freedom will get neither. A society that puts freedom before equality will get a high degree of both.

Economist Tyler Cowen has argued that though income inequality has increased within nations, globally it has fallen over the last 20 years. He argues that though income inequality may make individual nations worse off, overall, the world has improved as global inequality has been reduced.[169]

Patrick Diamond and Anthony Giddens (professors of Economics and Sociology, respectively) hold that 'pure meritocracy is incoherent because, without redistribution, one generation's successful individuals would become the next generation's embedded caste, hoarding the wealth they had accumulated'.

They also state that social justice requires redistribution of high incomes and large concentrations of wealth in a way that spreads it more widely, in order to "recognise the contribution made by all sections of the community to building the nation's wealth." (Patrick Diamond and Anthony Giddens, June 27, 2005, New Statesman)[170]

Pope Francis stated in his Evangelii gaudium, that "as long as the problems of the poor are not radically resolved by rejecting the absolute autonomy of markets and financial speculation and by attacking the structural causes of inequality, no solution will be found for the world’s problems or, for that matter, to any problems."[171] He later declared that "inequality is the root of social evil."[172]

In most western democracies, the desire to eliminate or reduce economic inequality is generally associated with the political left. One practical argument in favor of reduction is the idea that economic inequality reduces social cohesion and increases social unrest, thereby weakening the society.

It has also been argued that economic inequality invariably translates to political inequality, which further aggravates the problem. Even in cases where an increase in economic inequality makes nobody economically poorer, an increased inequality of resources is disadvantageous, as increased economic inequality can lead to a power shift due to an increased inequality in the ability to participate in democratic processes.[174]

The capabilities approach – sometimes called the human development approach – looks at income inequality and poverty as form of “capability deprivation”.[175] Unlike neoliberalism, which “defines well-being as utility maximization”, economic growth and income are considered a means to an end rather than the end itself.[176] Its goal is to “wid[en] people’s choices and the level of their achieved well-being”[177] through increasing functionings (the things a person values doing), capabilities (the freedom to enjoy functionings) and agency (the ability to pursue valued goals).[178]

When a person’s capabilities are lowered, they are in some way deprived of earning as much income as they would otherwise. An old, ill man cannot earn as much as a healthy young man; gender roles and customs may prevent a woman from receiving an education or working outside the home. There may be an epidemic that causes widespread panic, or there could be rampant violence in the area that prevents people from going to work for fear of their lives.[175] As a result, income and economic inequality increases, and it becomes more difficult to reduce the gap without additional aid. To prevent such inequality, this approach believes it’s important to have political freedom, economic facilities, social opportunities, transparency guarantees, and protective security to ensure that people aren’t denied their functionings, capabilities, and agency and can thus work towards a better relevant income.

The Economist wrote in December 2013: "A minimum wage, providing it is not set too high, could thus boost pay with no ill effects on jobs....America's federal minimum wage, at 38% of median income, is one of the rich world's lowest. Some studies find no harm to employment from federal of state minimum wages, others see a small one, but none finds any serious damage."[187]

General limitations on and taxation of rent-seeking are popular across the political spectrum.[188]

^Wojciech Kopczuk, Emmanuel Saez, and Jae Song find that “most of the increase in the variance of (log) annual earnings is due to increases in the variance of (log) permanent earnings with modest increases in the variance of transitory (log) earnings.” Thus, in fact, the increase in earnings inequality is in lifetime income. Furthermore, they find that it remains difficult for someone to move up the earnings distribution (though they do find upward mobility for women in their lifetime). See their “Earnings Inequality and Mobility in the United States: Evidence from Social Security Data since 1937,” Quarterly Journal of Economics. 125, no. 1 (2010): 91–128.

^Branko Milanovic (2012). The Haves and the Have-Nots: A Brief and Idiosyncratic History of Global Inequality. ISBN978-0465031412.

^Keen, Steve (2011). Debunking Economics - Revised and Expanded Edition: The Naked Emperor Dethroned?. Zed Books. p. 110. ISBN978-1848139923. The basis for this advice is the proposition that a person's income is determined by her contribution to production - or more precisely, by the marginal productivity of the 'factor of production' to which she contributes...The argument that highly paid workers - managers of major corporations, stock and money market traders, financial commentators, etc - deserve the high wages they receive compared to the less highly paid - nuclear physicists, rocket scientists, university professors, school teachers, etc. - is simply an extension of this argument to cover subgroups of workers. Members of the former group, we are told, are simply more productive than members of the latter, hence their higher salaries.

^(At the same time however, there is a strong connection between average income and health within countries. Example: Comparing average death rates in United States zip code areas organized by average income finds the highest income zip codes average a little over 90 deaths per 10,000, the poorest zip codes a little over 50 deaths and a "strikingly" regular gradient of death rates for income in between. source: Figure 1.4, Pickett and Wilkinson, The Spirit Level, 2011, p. 13, Authors: "What is so striking about Figure 1.4 is how regular the health gradient is right across society". Data from G.D. Smith, J.D. Neaton, D. Wentworth, R. Stamler, J. Stamler, "Socioeconomic differentials in mortality risk among men screened for the Multiple Risk Factor Intervention Trial: 1. White men.", American Journal of Public Health (2008) 98 (4): 486–96)

^Pickett and Wilkinson, The Spirit Level, 2011, pp. 306–9. Figure 2.2 found on p. 20 and this page

^the authors found a Pearson Correlation Coefficient of 0.87 for the index and inequality among 20 developed countries for which data was available. Pickett and Wilkinson, The Spirit Level, 2011, p. 310.

^a coefficient of 0.59 for 40 US states for which data was available (the index for US states did not include a component for mobility in its index). For both populations the statistical significance p-value was >0.01. Pickett and Wilkinson, The Spirit Level, 2011, p. 310.

^The Way Forward By Daniel Alpert, Westwood Capital; Robert Hockett, Professor of Law, Cornell University; and Nouriel Roubini, Professor of Economics, New York University, New America Foundation, October 10, 2011

^The relation between economic inequality and political inequality is explained by Robert Alan Dahl in the chapters The Presence of a Market Economy (pp. 63), The Distribution of Political Resources (pp. 84) und Market Capitalism and Human Dispositions (pp. 87) in On Political Equality, 2006, 120 pages, Yale University Press, ISBN 978-0-300-12687-7

Deneulin, Séverine; Shahani, Lila (2009). An introduction to the human development and capability approach freedom and agency. Sterling, Virginia Ottawa, Ontario: Earthscan International Development Research Centre. ISBN9781844078066.

Gilens, Martin (2012). Affluence and influence: Economic inequality and political power in America. Princeton, New Jersey New York: Princeton University Press Russell Sage Foundation. ISBN9780691162423.

Lambert, Peter J. (2001). The distribution and redistribution of income (3rd ed.). Manchester New York New York: Manchester University Press Palgrave. ISBN9780719057328.